The invention relates to variable-track wheels, and more particularly to power-adjustable variable-track wheels for agricultural tractors or like vehicles.
One known type of such wheels comprises a hub having a cylindrical periphery, at least three brackets circumferentially spaced around and secured to the hub in contact with its cylindrical periphery, and a rim to which there are secured helical rails each of which is slideable in a groove in one of the brackets, each groove housing a block which is moveable into and out of clamping engagement with the associated rail by the rotation of an eccentric pin journalled in a bore formed in the bracket and intersecting the groove. The driving wheels on opposite sides of a vehicle usually have helical rails of the same hand for ease of manufacture, and the track-width is adjusted by moving the blocks on one of said wheels out of clamping engagement with the rails thereon, causing the driving axle of the vehicle to rotate in the appropriate direction so as to screw the rim of said one wheel towards or away from the longitudinal centre-line of the vehicle as required until one of the brackets on said wheel contacts a stop adjustably secured to the associated rail thereon, moving the blocks back into clamping engagement with the rails, and then repeating the procedure for the other driving wheel. Due to manufacturing tolerances and/or eccentricities in the hubs and rims, which increase as tractors and their driving wheels tend to become physically larger, and due also to the tendency for the torques required to be transmitted by the driving wheels to become higher, we have found that it is difficult to produce a wheel in which, even when new, the rim can be effectively clamped in adjusted position, and even more difficult to achieve effective clamping when the components have become worn by use. It has been proposed to remedy these difficulties by inserting shims where necessary between one or more of the brackets and the cylindrical periphery of the hub. The object of the invention is to provide means for more simply and positively enabling the position of one or more of the brackets radially of the hub to be adjusted prior to securing said bracket or brackets to the hub.